Stumbling MAJOR ISSUES please help

[bdijanni]

Ok, I posted a couple of weeks ago about my stubling problems. I have read through everything on here and I can not figure out what to try next. I have a 1999 q45, with 101K great condition. When you drive the car it will have a weird slight stumble, sitting at a stop in drive you the brakes on, also with do it while driving and in park, sometimes when driving around 35-45 and trying to hold the car steady between those speeds it will stumble so bad that it will act like its not going to accelerate. you have to kind of let off the gas and hit it kind of hard to get it to go. it will also do it while in park, it will sit there and just stumble really bad, almost feels like a miss fire, The problem will happen alot worse with the AC on. The AC almost guarante's that it will make it happen.

Ok so what i've already tried: I did a full tune up. a can of bg44k.the used to have the check engine light on, when i got that checked out the parts store told me that it was saying that the right bank o2 sensor and the right bank knock sensor. Well I went and changed out the upstream o2 sensors which made the light turn off and it hasnt come back on yet its been about 300 miles since then, also made the stumbling happen alot less. but is still happening. especially with the AC.

Has anyone had this problem before and figured it out?? I read in some of the old threads where people were having simular problems, they tried all kinds of different things and no one ever reported the fix? Any help would be greatly appreciated... Thanks in advance

[Q45tech]

Lean misfire is usually the spark plugs, or gasoline quality especially if ethanolized fuel is used.

Unlike the 90-95 coils which almost never fail the newer cost cutting designs are less robust.

Finding a random misfire often takes a BRAIN, Training, and exotic test equipment unavailable to dealers. They see so few units not cost effective to buy $3-5,000 just to test coils and leads.

http://www.pc-oscilloscopes.co...d/554

http://www.pc-oscilloscopes.co...d/565http://www.pc-oscilloscopes.co...d/555

[Mike G]

Quite a frustrating pain, isn't it?

Unfortunately, I have had an auto or two that it seems all you do is throw $50 parts at it until it stops... My 01 "seems" to do this occasionally as well, I was going to turn to the Mass Air Flow and the Throttle Possition Sensor. Mine however is more of a slight anoyance at this point so I'm in no hurry (and the parts prices are too much).

--Mike

[bdijanni]

Yeah I was thinking that it might be a dead miss also, bit it does it at such weird times and how it is doing it makes me think that its not a missfire! I also changed out all the plugs, and no change the only thing that i didnt mention is that it did get better after I changed out the o2 sensors, but while i was under the car I noticed a transmission leak coming from the rear of the transmission right where the drive shaft meets the transmission. but the strange thing is that the wires and the wire cover plate are the only things that are wet, no other part of the transmission is wet everything other then the wires and the cover plate is dry. Now the wires and the plate are totally wet with transmission fluid. ALso I have a couple of stupid questions!

1. when checking the transmission oil, are you supposed to check it when the car is running or not? and theres fill marks for cold and hot? I thought that you were supposed to check with car running and at NOT (normal op temp)???

2nd? What is y33 and g50? which cars are these?

[96Qowner]

The leak is coming from your revolution sensor - typical.

zerothread?id=204402

You can find more threads about it by searching.

G50 is the 90-96 Q45. Y33 is the next series (yours).

[VA99Q45]

I have the same problem with my 99 q45.I think my problem is the clogged injectors. If I dump a can of BK44, it rides and idle supper smooth without any stumble. After the third tank of gas, it starts to do stumble again.

All of the injector ohm values are in the correct range ~11 ohm. I had the fuel injector flush, but it only help reduce the amount of stumble. My next step is overhaul my injectors.

I did get a check engine code, and it was for misfire on the third cylinder.

[maxnix]

I did get a check engine code, and it was for misfire on the third cylinder.

Then switch your coil pack with another and see if the next code follows the coilpack or stays at the cylinder (injector or plug).

[VA99Q45]

Then switch your coil pack with another and see if the next code follows the coilpack or stays at the cylinder (injector or plug).

That is a good suggestion. But I already did that. I swapped the coilpacks between 1 and 3, but it never gives me another code after.

I have eliminated the coilpack as a possible problem because if I dump a can of BK44 in the gas tank, everything run smooth.

My hunt right now is that the clogged injector on cylinder #3.